Whereas the reliability of prophylactic devices such as condoms has always been important, the prevalence of AIDS and the alarming increase in unwanted pregnancies has placed even greater emphasis on detecting holes through which body fluids may pass. At the same time, it is important that the testing for holes be done as economically as possible. Ideally, no defective condoms should pass a test for holes and no acceptable condoms should fail it. It is the understanding of the inventors that the FDA requires testing for holes as small as 10 microns.
A number of testing methods are available. They include a water leak test in which the condom is filled with water and an operator visually checks its outer surface for water droplets. Small holes in the condom result in extremely small water droplets on the surface. These droplets are difficult to see even if the hole location is known before the test is performed. Under actual operating conditions, the failure to detect such a small water droplet could result in the acceptance of a defective condom. Unless extreme care is used, water droplets can be inadvertently deposited on the condom so that acceptable condoms are rejected. Furthermore, it is difficult for an operator to continue to keep a sharp eye out for the droplets. In addition to these difficulties, the inspection of a condom for droplets takes a long time.
Holes can also be detected by electrical methods. In a "wet test", a condom is stretched over a mandrel of conductive material and immersed in a conductive aqueous solution. A low voltage is applied between the mandrel and the solution so that the flow of current in the circuit thus formed indicates a hole. In a "dry test" method, the condom is stretched over a conductive mandrel and conductive brushes or a fine steel screen is placed in contact with the outer surface of the condom. Voltage is applied between the mandrel and the brush or screen so as to produce a current if there is a hole in the condom. But such methods do not work well for condoms made of certain non-latex material, such as polyurethane, for example.
U.S. Pat. No. 5,129,256 describes a method and apparatus for testing condoms by mounting them on a hollow porous mandrel, drawing a partial vacuum in the space within the mandrel and monitoring the interior of the porous mandrel for gas flowing through its walls with a vacuum pressure transducer. It is indicated that preferably the mandrel have an outside diameter that is less than the inside diameter of a condom. The pore openings in the wall are distributed substantially uniformly over its external surface and preferably have a median diameter ranging from ten to fifty microns with a preferred median diameter of twenty microns. The porous part of the mandrel is comprised of a cylindrical body that is closed off at one end, has a wall thickness between 0.04 to 0.50 of an inch and a void volume between 35% and 60%.
If the mandrel is made by sintering particles, fine pores are desired because the dimensions of the walls between pores at the surface of the mandrel are smaller and thus less likely to block a hole in a condom that is stretched over it.
In an invention set forth and claimed in U.S. Pat. No. 5,517,849, a condom or other prophylactic device is tested by mounting it within an hollow central portion of a testing device having a porous liner of a preferably corresponding shape and establishing a differential in pressure between the inside of the condom and the space outside of the porous liner. The differential can be obtained by increasing the pressure in the space inside the condom while the space outside the porous liner is at a predetermined pressure such as atmospheric pressure or by creating a partial vacuum outside the porous liner while the space inside the condom is at atmospheric pressure. The differential in pressure is established during a first period, in which the condom is inflated. The pressure within the condom is allowed to stabilize during a second period, and the rate of change of the pressure differential between the interior of the condom and outside the porous liner is tested within a third period, for determining if it exceeds a given value so as to indicate the presence of a leak through a hole in the condom. During the second and third periods, in one embodiment of the invention, gas passing through a hole in the condom increases the pressure within a confined region about the porous liner so as to provide an integrated effect, if the interior has a higher pressure or if the confined space outside the porous liner and condom is at a lower pressure than interior to the porous liner. Pressures are tested at the beginning and end of the third period, and the change during each test is compared to previously determined calibration limits to determine the acceptability of the condom.
In accordance with an aspect of the invention of the aforesaid Patent, the determination made during the third period referred to above as to whether the pressure in the confined space or region outside the porous liner and condom is increasing rapidly enough to indicate a leak is made by comparing it with a standard pressure. If it is greater than a predetermined value, a leak is present, but if it is not greater there is no leak. This is a more accurate method than making an absolute measurement of the pressure external to the condom with a transducer.
As previously noted, from a theoretical viewpoint, the smaller the pores at the surface of the porous liner, the smaller the holes that can be detected in a condom. In accordance with an important aspect of this invention, the size of pores in the portion of the porous liner that will be adjacent the body portion of a condom during a test is small enough to detect holes of an acceptable minimum size at any point in the condom.